Haematopoietic stem cells.

Considerable efforts have been made in recent years in determining the composition of the cell types that constitute the human haematopoietic stem cell (HSC) compartment. These studies have emphasized the heterogeneity of the human HSC in terms of proliferative and self-renewal capacities. Recent studies have indicated that CD34 is not the universal marker of all human HSCs. New markers for purifying HSCs have been described. A number of genes that regulate the formation, self-renewal, or differentiation of HSCs has been identified. The elucidation of the molecular phenotype of the HSC has just begun. Finally, an unexpected degree of developmental or differentiation plasticity of HSC has emerged. This review summarizes all the recent advances made in the human HSC field and examines the impacts that these discoveries may have both clinically and in understanding the organization of the human haematopoietic system. Copyright 2002 John Wiley & Sons, Ltd.